cant tell much from that distance.. but what happened to the two that were removed.. leaving the blank spaces??? this looks like a slow progression that has been going on for a while... have you ever had a soil test done .. what did the dead ones look like ...underground ... this is where you tell me you just bought the house ... whats the deal with the lawn green under the camera.. and near dead out by those plants ... how bad has drought be the last 2 seasons??? ....since they are mature plants.. i would think heat is not an issue.. they have been there a rather long time .... is there a mulch volcano on the tree.. or is that a camera trick ... so many questions.. so little time ken

Was it grafted? It probably reverted back to its root stock (it happens) what nursery did you get it from? They should replace it for you immediately if not first thing next season. This happened to me with one of my Austins Wildeve. It was NOT the flower I purchased (came out white and small). Austin's in Texas is sending me a replacement but I have to wait until next Jan. I hate waiting but I guess these things happen.

Start your search for why with a good, reliable soil test. Contact you local office of the University of Massachussets USDA Cooperative Extension Service to have a base nutrient load and soil pH level test done. Then dig in with these simple soil tests to see what you have; 1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top. 2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up. 3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart. 4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell. 5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy. Pieris need the same soils and growing conditions as the Rhododenron family, a soil well endowed with organic matter that is evenly moist but well drained and has a lower than normal soil pH, in partial shade. The more sun exposure they have the more soil moisture they need. Here is a link that might be useful: UMASS CES

Before doing any more, or allowing people that do not know what they are doing spray something else, tak samples of this shrub and place them in a sealable plastic bag and take it to your local office of the University of Florida Cooperative Extension Service. They will identify what the problem is and what the appropriate means of control might be. http://sfyl.ifas.ufl.edu/map/index.shtml